fix: add useExperimentalRetryJoin: true to worker node spec

[jackfrancis]

What this PR does / why we need it:

This PR adds the useExperimentalRetryJoin: true kubeadm configuration to the worker node spec to prevent scenarios described in issue #832 from prevening nodes joining a cluster.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #832

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

add useExperimentalRetryJoin: true to all KubeadmConfigTemplate resource specs

[k8s-ci-robot]

Hi @jackfrancis. Thanks for your PR.

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[CecileRobertMichon]

/ok-to-test

[CecileRobertMichon]

two last ones:
https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/master/templates/flavors/system-assigned-identity/system-assigned-identity-md.yaml#L48
https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/master/templates/flavors/user-assigned-identity/user-assigned-identity-md.yaml#L50

[jackfrancis]

@CecileRobertMichon curious, why not these two?

https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/master/templates/flavors/external-cloud-provider/patches/external-cloud-provider.yaml#L39
https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/master/templates/flavors/system-assigned-identity/patches/system-assigned-identity.yaml#L2

I'm inferring that those patch configs will require a kubeadm restart of some kind to actually load the config diff, right? Is the retry foo we're adding here only valid for node registration operations, and those two patch configs don't engage node registration flows?

[jackfrancis]

(though both of those patches include a joinConfiguration.nodeRegistration config...)

[CecileRobertMichon]

You're right, we want it there too! Basically every kubeadmConfigSpec should have it, control planes and worker nodes alike.

[CecileRobertMichon]

lgtm, @jackfrancis please squash the commits and add a release note

[devigned]

lgtm

[CecileRobertMichon]

let's also mark this as "Fixes #832" since it solves the issue for now

[CecileRobertMichon]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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